This disclosure relates to compositions and methods of preparation of blends containing polyesters and copolyetherester elastomers, methods for their manufacture, and articles thereof. The elastomer blends are derived from recycled polyesters, in particular polyethylene terephthalate.
Polyethylene terephthalate (also referred to as “PET”) is a polyester of terephthalic acid and ethylene glycol that can be obtained by the polycondensation of dimethyl terephthalate with ethylene glycol, and also terephthalic acid with ethylene glycol or ethylene oxide. PET exists both as an amorphous (transparent) and as a semi-crystalline (opaque and white) thermoplastic material. Generally, it has useful chemical resistance to mineral oils, solvents, and acids but not to bases. Semi-crystalline PET has good strength, ductility, stiffness, and hardness. Amorphous PET has better ductility but less stiffness and hardness. PET is used to make bottles for soft drinks and other household and consumer products. Generally, PET has many uses and several large markets. For this reason, the volume of PET manufactured is large and growing.
Unfortunately, despite recycling efforts, billions of pounds of PET are still dumped into landfills annually all over the world. Other PET that is not reused is incinerated. The PET that is disposed into landfills creates significant waste. The incineration of PET also wastes a significant resource that could be used more effectively.
Copolyetheresters, sometimes referred to as TPEE elastomers, are a special class of elastomeric materials. These materials exhibit thermoplastic processability on conventional molding equipment and exhibit the elasticity and resistance to impact and flex-fatigue of conventional cured rubbers. The combination of properties is obtained due to the result of the phase separation between the amorphous polyether segments (polyether blocks) and the crystalline polyester segments (polyester blocks) of the copolymer molecule. Because the immiscible segments are copolymerized into a single macromolecular backbone the necessary phase separation that occurs results in discrete domains with dimensions on the order of magnitude of the polymer chain. Thus, the polyether forms soft, amorphous domains that are physically crosslinked by the ‘knots’ of crystalline, polyester, domains. That is, the amorphous soft blocks provide the elastomeric properties of flexibility and low temperature impact while the presence of the crystalline hard block results in discrete melting points, heat and chemical resistance, and mechanical strength. These materials are also commonly characterized by a lower temperature brittleness point than conventional rubbers, resilience, low creep, and very good resistance to oils, fuels, solvents, and chemicals.
Although molding compositions using conventional polybutylene terephthalate (PBT) copolyetheresters are useful to many customers, these molding compositions may lack the ability to strike certain property balances, for example the combination of heat aging resistance with good flexibility, and/or the combination of chemical resistance to organic solvents with good flexibility.
To that end, blends of polyesters or polyester copolymers with copolyetheresters derived from recycled (scrap) PET create the ability and flexibility to create desired property balances for targeted applications.
Unfortunately, known solutions for making copolyetheresters do not offer effective ways of using PET scrap that meets today's customer needs. GB 1500577 discloses the treatment of scrap PET with an alkylene glycol in an amount of 0.1 to 5 times the weight of the scrap PET. In a preferred embodiment, GB 1500577 discloses that these materials are heated at 200 to 250° C. to reflux the glycol for a period of about 8 hours or until the solution becomes clear. The first portion of the glycolization step is preferably carried out at atmospheric pressure and the final portion preferably is carried out at a pressure of less than 0.5 mm Hg.
The examples of GB 1500577 disclose that “it will be observed that the modulus at various percents elongation for the product produced in accordance with the present invention is quite consistently about half of the modulus of the product produced in accordance with Example 4 of U.S. Pat. No. 3,701,755 when the ingredients are of closely comparable amounts.” Example 4 of U.S. Pat. No. 3,701,755 discloses, that “12.17 parts of bis(2-hydroxyethyl) terephthalate, 20.0 parts of PTMG (molecular weight 1800) and 0.014 part[s] of zinc[ ] acetate were charged into a reaction vessel at 200° C. The pressure was gradually reduced while heating, and the polycondensation was conducted under a high vacuum of less than 1 mm. Hg for 80 minutes. The obtained copolymer had a melting point of 208° C. and ηsp./c.=3.03.” When treated and modified “in ways known for treating segmented copolyetherester elastomers,” GB 1500577 discloses that its product is useful in the production of such items as garden hoses, industrial hose material, industrial tires, and tennis shoe soles.
Today's demanding customer needs often require elastomeric products having excellent performance properties. Although GB 1500577 demonstrates a way of using scrap PET, elastomeric polymers that exhibit about half of the modulus of monomer/bis(2-hydroxyethyl) terephthalate-based materials are not acceptable to many customers today. Solutions that require additional modification would not be practical or feasible for manufacturers today.
Other attempts directed to using post-consumer polyesters such as scrap PET have been directed to methods and devices designed to recover polymers or polymeric components obtained during the depolymerization of polymers. U.S. Pat. No. 6,162,837, for instance, discloses a method and device for recovering linear polyesters, such as PET and PBT, from polyester waste of the most varied form, in a continuous manner, in which undried or not dried-through waste is melted, the polymer chains being hydrolytically degraded by adhering moisture, and in which diol, corresponding to the basic constitutional unit of the polymer, is added to the melt resulting in glycolytic degradation, and the melt so treated is further condensed to the desired degree of polymerization. EP 1437377 discloses a process that involves a depolymerization reaction of used PET bottles with ethylene glycol, recovering dimethyl terephthalate (DMT) by ester interchange reaction with methanol, obtaining terephthalic acid by hydrolysis of the recovered DMT, and manufacturing a PET polymer that can be used for manufacturing PET bottles again by using the terephthalic acid. However, such solutions do not address the need to make copolyetheresters that have suitable commercial properties from scrap PET, e.g., copolyetheresters having properties comparable to PBT-based copolyetheresters.
For the foregoing reasons, there is an unmet need to develop improved elastomer blends of polyesters and copolyetheresters derived from recycled PET which exhibit excellent performance properties.